1998 Z71 SOFT BRAKE PEDAL SOLVED

Discussion in 'Axles + Brakes' started by DESSERTNOVA, Mar 13, 2018.

  1. DESSERTNOVA

    DESSERTNOVA Newbie

    Messages:
    14
    Likes Received:
    15
    Joined:
    May 30, 2017
    Location:
    North Granby CT
    Hello All,
    I recently purchased a 1998 z-71 that was experiencing the soft brake pedal issue. After bleeding a gallon of brake fluid through the system with pedal pump, vacuum bleeder, abs firing and gravity nothing helped. I then re-adjusted the rear brake shoes to the point it was almost impossible to put the drum back on and bang, solid pedal and awesome brakes. I guess being an old school GM gear head and always adjusting drum out to a light scrape is not sufficient in this application. Hope this helps anyone else experiencing this aggravating issue.
     
  2. redfishsc

    redfishsc Apparently can't own too many Suburbans

    Messages:
    377
    Likes Received:
    114
    Joined:
    Nov 7, 2016
    Location:
    South Carolina
    Yeah ive found that the star adjusters on the drums are only sufficient for keeping them adjusted just enough that they still function.

    I need to adjust the ones in my 2wd Sub, i just put on a new Master cylinder and had the brakes auto-bled with a scan tool. Results were very good but i think the pedal could be even better if i adjusted the shoes out a little more
     
  3. DerekTheGreat

    DerekTheGreat I'm Awesome

    Messages:
    428
    Likes Received:
    104
    Joined:
    May 23, 2016
    Location:
    Michigan
    You may want to be careful with over adjusting them.. I did that on my Town Car, pedal felt great but the drag was such I could smell burning brakes at stop lights so I had to back off.
     
  4. DESSERTNOVA

    DESSERTNOVA Newbie

    Messages:
    14
    Likes Received:
    15
    Joined:
    May 30, 2017
    Location:
    North Granby CT
    5 thousand miles since, this was actually the instruction from GM master tech. I believe there is a special snap on gage to set the pads to the drum size within a few thousandths of inch-but I have not confirmed the gage existance.
     
  5. RichLo

    RichLo I'm Awesome

    Messages:
    656
    Likes Received:
    186
    Joined:
    Jan 6, 2015
    I've heard of two different ways of auto-adjusting them. Either hit the brakes hard in reverse or have a functional parking brake that you use regularly. The two methods dont interchange, its the way the drums are designed, so either one or the other. If reverse doesn't work then you need to fix your parking brake cable.
     
  6. Lanny

    Lanny OBS Enthusiast

    Messages:
    64
    Likes Received:
    14
    Joined:
    Feb 9, 2018
    Location:
    Saint Albans, VT
    Reverse is the way to adjust them from the factory when everything is working. However, if something wasnt working you can still change the screw by hand.
     
  7. RichLo

    RichLo I'm Awesome

    Messages:
    656
    Likes Received:
    186
    Joined:
    Jan 6, 2015
    Thats the way some trucks are others like mine (93 k1500) needs to have a functional parking brake to auto-adjust. I forgot where the cutoff was but its an either-or situation.
     
  8. Lanny

    Lanny OBS Enthusiast

    Messages:
    64
    Likes Received:
    14
    Joined:
    Feb 9, 2018
    Location:
    Saint Albans, VT
    My guess is it changed in the 94 to 95 days? I really have no idea. I only have experience with the late model (98) and a few earlier ones.
     
  9. evilunclegrimace

    evilunclegrimace I'm Awesome

    Messages:
    295
    Likes Received:
    94
    Joined:
    Sep 18, 2017
    Location:
    pennsylvaina
    The brake design on the GMT-400 trucks is dependent on the model. !500/2500 with 10 x 2.25 rears are what GM refers to as Leading/trailing brakes. what this means is that both shoes are the same size, with this design there is a lower anchor point that prevent the shoes from rotating into the drum when applied. The purpose of using this design is to allow the rear brakes to apply and release very quickly due to having ABS.

    Leading/trailing brakes have the adjuster mounted towards to top of the shoe as it's only purpose is to allow adjustment of the shoes, it plays no part in transfer of power from the shoes to the drums. These brakes are adjusted when the E brake is applied.


    On 1500 series trucks with 11.16 brakes and on the 2500/3500 trucks with 13" rear brakes ( both 3" and 3 1/2" wide) the Brakes are of the duo/servo style in which there are two different length shoes. There is a short shoe and a long shoe. The short or primary shoe goes toward the front of the vehicle and the long or secondary shoe goes toward the rear of the vehicle.
    This type of brakes has an upper pivot and the adjuster is near the bottom of the shoes and it serves two functions. One is to allow the automatic adjustment of the rear brakes when the vehicle is driven in reverse and the brakes are applied, the second is to transfer force from the shoes to the drums by allowing the shoes to rotate with and into the drum allow for higher braking force due to the "servo" action.

    This type of system was also used with ABS brakes but the rears were not able to apply and release as quickly as the Leading/trailing brake system and it was problematic under heavy braking.
     
    Last edited: Mar 19, 2018
    Bob L and RichLo like this.
  10. RichLo

    RichLo I'm Awesome

    Messages:
    656
    Likes Received:
    186
    Joined:
    Jan 6, 2015
    Thank you for that clarification!!!

    So 1500 and 'heavy half' 2500 (6-lug) needs a functional parking brake

    and 8-lug 2500 and 3500 can just brake in reverse.
     

Share This Page